Method of making a papermaker&#39;s felt



No Drawing. Application-April 5,1957 Serial No. 650,832

4 Claims: (Cl. 28-72) The present inventionrelates to papermakers feltsand a method forthe manufacture thereof and moreparticularly topapermakers felts madefrom synthetic fibers and a method by which suchfelts may be manufactured. The-papermakers felts to whichthis inventionis directed are those which are used at any stage in the wet end oraheadof thedriersiofa papermaking machine: The-term papermaking machineincludes machines which are used for the manufacture of cementandasbestos-cement-products-,- wallzboard, roofing felts, pulp laps andsimilar and relatedproducts. Such felts customarily have: been madefrom; natural -wool l or occasionally from ablend of natural wool andsynthetic fibers. These" felts' are hereinafter referredto' aspapermakers. feltsor as papermakersv wet felts.

Papermakers wet felts are usually woven fabrics which have been fulledto cause the wool fiberstherein to felt. In the manufacture thereof fromwool or a blend of wool and synthetic material which contains sufiicientwool to render the fabric fullable, it has been customary to weave afab'ric of a given width and to full it to a width ap-- proximatelyone-half the woven width while maintaining the woven lengthapproximately the same throughout the operation. In this manner thewoven material assumes the desired firmness in texture" and the feltingof the. wool fibers with one another gives the felt a high degree ofdimensional stability under the conditions of use. The fulling operationalso cl'oses up the fabric givirig it'the ability to retain" the fibersof the paper while being sufiiciently porous to permit rapid removal ofthe water in the freshly laid paper. Beyond this, the natural woolpapermakers felt will remain resilient while wet and thu's hastheability to pick up a freshly laid'web'of paperfrom the wire andconduct it through the presses. This highly exacting combination ofrequirements has heretofore been-met only we natural wool fabric or onein which natural wool has been blended with a limited amount of otherfibers and in each instance ithas been es's'entialthat the fabrics becapable of fulling;

According to the present invention, I providea' method for manufacturingentirely suitable papermakers felts having great dimensional stabilityand having a' 'life far in-excess' of 'that achieved by the best ofwoolen papermakers felts, my new felts being made substantially whollyfrom synthetic materials or blends thereof which are not capable offelting and which heretofore have been used only in limited amounts incombination with large-pen centages of wool irlthe manufacture ofpapermakers felts. According to my process, papermakers felts may bemade entirely or substantially entirely from fibers or blends of. fiberswhich have-dry tensile strengths substantially above 20,000 pounds persquare inch, which is-the average dry tensilezstrength of natural wool,and which. do notlose tensilestrength appreciably when wet and whichqualities are: nylon and fibers derived from polyvinylidene r 2,821,771Patented Feb. 4;, 1958 chloride. and acrylonitrile, copolymers of.polyvinylacetate, polyvinylchloride andpolyacrylonitrile andcondensation products of terephthahc acid and ethylene glycol. The tradenames. "saran, Orion, "dynel" and Dacron. are used to identityparticular fibers within this group.

Many syntheticfibers suchlasthose enumerated above are supplied by themanufacturers thereof in the form ofa staple fiber which has beenmanipulated or treated by the manufacturer to resemble,. as closely aspossible, anatural woolfiber. buchfibers are generally identified as"crimped" although the particular conformations formed inthe fibers thusidentified may comprise crimps,,crinltles, curls, spirals, indentationsor serrations in one or more lhus, tor. example, nylon is supplied as astaple fiber having, a. diameter and staple length t'alling within therangeot' diameters and staple lengths encountered in natural wool. Whilethese nylon fibers do not have the charaeteristicot' felting, theyaresupplied in a delustered tormtan'd with a large'num'ber of sharpcrimps throughoutrtheir individual lengths which are permanentindividual fibers will remainso fiber willtexhibitsubstantially the bulkand springiness of wool 'and although it has a moderate initialshrinkage, it does not: exhibit the tendency to felt. This-makes suchmaterialzhig-hly desirable as a substitute for wool in manyfields-wherein progressive hardening and t61'lSIiC10f wool isundesirable. 'ihe lack of this characteristic, however,- has renderedsuch fiberwholly unsuitable for the manufacture of papermakers felts inaccordance with known processes. following particular made wholly fromsuch synthetic fibers.

The process and product of the presentinvention will be first describedin general terms to enable those skilled in the art to manufacturepapermakers felts from a relaselected for the manufacture ofpapermakersfelts having certain desired characteristics. Thus, syntheticresin staple fi ers are available in variousstaple lengths and invarious engage one another in a relatively permanent relationship, thuscontributing to dimensional stability of the final product.

.carding and spinning,

makers felts may be made wholly from synthetic resin as of the date offiling of fibers exhibit no definite 'equal to the corresponding ratioin natural wool which averages about 77%, that the fiber retain a largedegree of its original resilience when wet and that the selectedsynthetic fibers have an abrasion resistance at least equivalent to woolwhen wet. The selected fiber must also have the property of taking apermanent set when subjected to heat treatment within the ranges of from150 F. to 350 F. Furthermore, any crimping or curling imparted to thefibers should be permanent in the sense that they will not straightenout under the tensions found in weaving or finishing or heat treatmentor under continued operation while wet at the temperatures encounteredby papermakers felts upon a papermaking machine or during such cleaningor reconditioning operations as are normally practiced. Otherwise thefabric will lose its bulk and resilience.

In the manufacture of paper the advantage to be gained by the decreasein viscosity of water through the application of heat is recognized andin many cases, temperature of the paper stock is raised for thispurpose. Temperatures rarely exceed 140 F. for economic reasons althoughit is conceivable that temperatures ranging from 33 F. to 212 F. mightbe encountered in the normal manufacture of paper. In any event the feltis not at all likely to be subjected to temperature about 212 F. and forpractical purposes a felt set at 212 F. or slightly higher, as forexample from 212 F. to 240 P. will be quite adequate for use on machinesused in the manufacture of paper, asbestos cement products, wall board,lap pulp and similar products.

Crimped nylon, Dacron or Orlon" fibers will retain substantially theiroriginal crimped form throughout manufacture and use of a papermakersfelt made from such materials and they have a ratio of wet strength todry strength considerably higher than natural wool. the case of saranfibers there are two forms presently available which fall within thegeneral classification of crimped fibers. One of these is identified bythe manufacturer as crimped and the other is identified as curled.Apparently or processing, the saran fibers identified as crimped do nothave sufficient stability under the conditions met in the manufactureand use of papermakers wet felts while the saran fibers identified ascurled have satisfactory stability. In the appended claims the wordcrirnped is used in the general sense so as to include the curled saranfibers having the other characteristics set forth in the claims.Cellulosic fibers such as rayon or cellulose acetate are Whollyunsuitable because of lack of strength, wet or dry, as well as theirlack of characteristics leading to dimensional stability under theconditions herein involved.

It is desirable that the synthetic resin fibers exhibit at least amoderate amount of initial shrinkage when a woven fabric made therefromis subjected to heat in the presence of moisture as by immersion in hotwater or exposure to wet steam. When hot Water is used any suitableadditional swelling agents may be added if so desired as is customary inthe shrinking of fabrics. This characteristic is exhibited by the nylon,Dacron fibers ident'fied hereinabove as otherwise suitable for use inthe present invention.

The selected synthetic fiber or blend of such fibers may be carded andspun into yarn in accordance with the technique ordinarily employed inthe carding and spinning of natural wool fibers. The yarns may betwisted and plied in any of the manners desired for particular due todifferences in manufacture final results. The warp and weft yarns may beidentical or may difier from one another in any of the respects alreadywell known in connection with the weaving of papermakers felts fromnatural wool.

The type of weave may be selected at will and excellent results havebeen had with plain weaving as well as with twills, etc., commonly usedfor producing papermakers felts of various grades and for variousintended uses. In view of the fact that only a moderate initialshrinkage can be expected and the fabric cannot be fulled, the ordinarytechnique of weaving the fabric relatively loosely and shrinking andfulling it will not produce a fabric having the necessary finalqualities. I have found that desired final construction may be achievedby supplying a proportionately greater number of warp ends on the onehand and so operating the loom on the other hand as to bring about aproportionately higher pick count to compensate for the lack of fullingquality. Thus the take up motion and the motion of the lay should be soadjusted that successive picks are beat up with relatively greater forcethan would be applied in the manufacture of a substantially identicalfinal product from fiber including sufficient natural wool to render thesame fullable.

Preferably the length of the synthetic papermakers felt of the presentinvention is maintained and the effect of such shrinkage as thesynthetic fibers may produce is chiefly confined to a reduction in widthof the finished felt. Thus, in the case of a felt which is to bespliced, the woven length is the warp length and it is this dimensionwhich is maintained so that shrinkage occurs only along the filling.When the felt is woven endless the filling length becomes the finishedlength and in that case shrinkage will be chiefly confined to the warpyarns while the filling threads are maintained substantially at theiroriginal length. With these considerations in mind, it will be apparentto those skilled in the art that in accordance with the presentinvention appropriate variations in the weight of yarn, count of warpends and picks and in the degree of beating up may be resorted to toproduce finished felts of widely varying specifications. Specificexamples of endless and spliced felts will be set forth hereinbelow.

After the fabric has been woven from the selected synthetic resinfiberor blends thereof, it is shrunk by heating in the presence ofmoisture as by placing it in relaxed condition in water which ispreferably heated to a temperature sufnciently to induce relativelyrapid initial shrinkage. To the same end it may be exposed to anatmosphere of steam at or near normal atmospheric pressure. If it isdesired to maintain the length of the felt substantially constant and torealize the major shrinkage in width, the felt is maintained undertension only in the direction of its length while permitting shrinkagein the cross-wise direction. A considerable amount of shrinkage can beachieved with any of the synthetic resin fibers set forth above assuitable for use in the present invention. While in some instances thefibers themselves 3 will exhibit a very small amount of shrinkage, thewoven Orlon and I result of the twisting and fabric will shrinkconsiderably more as a tensioning of the yarns during spinning, weaving.

After the initial shrinking the fabric is dried and during the dryingoperation the fabric is subjected to an elevated temperature for aperiod of time sufficient to not only remove any moisture remaining fromthe immersion or steaming thereof but also to induce a permanent set ofthe synthetic resin fibers in the positions and configurations in whichthey find themselves when the felt is held at the desired finaldimensions. The drying apparatus may be essentially the same as thatheretofore employed in the drying of natural woolen felts and usuallycomprises a heated drum and an idler roll spaced therefrom full lengthof the felt may be shrink'age thusefieeted many natural'themanu-factureof a nylon wiI lbe maintained at about 220 be left incontact therewith long enough for evaporaf d 'While inthemanufaeture ofe i I A felts it is customary -to rotate the drying drum continuously,and thus to pass'the feltcontinuously thrjoughan endlesspath, it hasbeenfound preferable in the drying] and setting of the synthetic felts ofthe present invention torot'ate the drying drum in steps. Each incrementof advance imparted to the felt in successive steps-is approximatelyequal to the length of felt which is ex-posed in direct contact witht e'heated drying drum. In this manner, each successive area of the felt maybe maintained in contact-with the surface jof the heated drum foraperi'od of time sufficient teary the felt and s o'ftejn the-fiberssomewhat so that they "will relax into the shapes'and positions assumedat that/time. The felt is then moved by rotating the drying drum tobring a new increment thereof "into contact with the drum. Theinerementleaving the drum is thus given an opportunity to"'cpol"a nd"the fibers therein will assume a'set which "willbe retained solong asthe felt is not subjected to a temperature a roaching the temperature atwhich the set" was established.

The drying oper'atio'hjust described-causes further shrinkingh'r thefabric in the filling direction. The plus the initial shrihkagedescribedabov wil he by thepartictilar fibers from which the fabric is woven.rot-example, =an-y'lon fiber which will shrink only about 2whenfrelaxed'inhot water maybe used for the manuf'a'c 'ture of apapermakers felt as described herein and the fi'n'ished *fabr'ic willhave-shrunk by asm-uch as from to=40% iritht-z direction of t efilleryarns.

The temperatures at which drying andsettin'g occur 'may be varied atwill in accordance with the particular fiber 'ojrblend of fiber used andin accordance with any ticul'ah'con'tirtiorfs to which a felt maybesubjected in further" processing or in ultimate use. For example,

1 W001 felts are impregnated with a therino setting resin andheated toset such resin during the manufacturing operatidns. In some instancesthe thermosetting resin requires heat treatment'at "about 300 F. to When"such materials are' incorporated into a *feltm'ad'e in accordance withthe present invention and jsu'eh higher temperatures are appliedthesynthetic resin fibers will'tak'e the permanent set, herein described,at the highertemperature;

-A lso, whether or not the :feltis impregnated, it may be "desired tohave the felt withstand some particular tern- 'p'erature to which itwill be subjected in use. In such ieven'tthe felt is set "at atemperature somewhat above that particular temperature. Ordinarily apaperrnakers wet felt may be set at or slightly above the boilingtemjrerature'of wat'er and itflwill maintain its-desirable characjterrstcs throughout it's life in the usual papermaking "b2 fio S h St p" atdiv e t s lto the p e ent n enayfbeav'ailed of to set the fibersasdescribed. Th drying drum described above is normally heated by is am,While'the fibers may be dried and set at a temperature as'low as about150 F., for practical purposes felt which will be subjected as ordinarypapermaking conditions, the drum preferably -F. and each increment tionof all of the water and for the dried felt to assume approximately thetemperature of the 'drum. The fibers will thus be set at about 220 F.and the finished felt will be entirely suitable for normal papermakinguses wherein it will not be subjected to temperatures in excess of about2-12" F.

If the feltis to be impregnated with a thermosetting resin or if it isdesired that itwithstand higher temperaturesit may; be passed throughfurther heating devices {maintained at suitable. temperatures. In thecase of was. he .maaia am emp ature sho ld not s zy x greatly in excessof the shrinkage exhibited *w'o'ol felts has been exceedingly short.

ceed about 350" F. if all of theoriginal characteristics of the fiberare'to be preserved.

The selection of the drying and setting temperature "for synthetic resinfibers other than nylon may be governed by the same considerations. Thetemperature must be at least highenough to set the particular fiber orblendbf fiber and it should be sufiiciently high to condition the:felt'f'or the use which it will encounter. The maximum temperatureshould not exceed that at which'the original desired characteristics ofthe fiber or blend might belost.

Felts made wholly from synthetic resin fibers in 'ac- 'cord'ance with*the present invention have successfully de'mbnstrated their utility onpaper machines ofyarious types in connection with *the production ofwidely differing grades-o'f-paper-as Well as in'the production-of otherrelated products such as those-made from asbestos cement aha'wallboard's-and thelike made "from ditferent types of furnish. In some0f these instances theffurnish contains materials-ofhigl-ily abrasivenatureand the life of natural The felts of the pr'esentinvention notonly have adequately demonstrated the greatly increased tensile strengthand life whieh might be expected as a "result of the substitutionofsyntheti'cresin 'fibers having greate'r tensile strength and abrasionresistance than natural wool, but also exhibit desirable 'grea'terporosity and have been completely satisfactory in dimensional stabilityand ease of cleaning and maintenance.

Throughout the specification, emphasis has been laid upon thefact thatin accordance with the teachings'h'ereof, it is possible Eto makepapermakers wet felts by 'weav- *in'g afabric from yarns consistingwholly of a particular synthetic resin fiber or a blend of two or moresuch fibers. Obviously minor amounts o-f-otherfibe'rs, including naturalwool, -m'ight be blended therewith without departing from theessentially novel features of :this inve'nti'on. The felts heretoforemade from blends ref natural and synthetic fibers have always containedsufiicient natural wool fibe'rsto render the fabric capable of beingful'led whereas the felts of the present invention c'onta'in noin'atural wool fibers or, 'at most, insufiicient quantity thereof toma'kethe fabric fullable. Thelprocess :of the present invention providesfor the-production 0f pap'e'rmakers" felts from fibers whichareessentially incapable of 'felting and the product of the .present inveation is a pap'ermakers felt made in the :form ofa woven fabric which isessentially incapable of fulling.

Specific examples of papermakers felts and of the :process for producingthe same will now be given and, for purposes of illustration,- therealso will be ig-iven-a description of theip'rocess and product resultingfrom the manufacture "of a natural wool felt having substantially thesame final specifications.

Example L A papermakers felt was :made from fiber comprising crimpednylon staple fiber havinga staple length of 3 :inches and a.fiber'diameter lying within the range of fiber diameters encountereduinnatural wool. Such fibers have a dry tensile strength of about 58,000pounds :per square inchand a wet tensile strength of about 56,000 poundsper square inch. Each fiberhatl been sharply and permanently crimpedthroughout its length to the extent that when straightened out undertension each fiberis approximately four inches in length. The fiber wascar ed, spun and twisted intoy'arn in accordance with ordinary.technique applicable to natural wool fiber. Yarn thus made weighing 700*grains per 100 yards, in 'the grease, was used for both warp and fill.-A reed having 7 dents per inch was used with two Warp ends per dent.The takeup'mechanism and lay were adjusted to supply "1'6 picks per:inch in a conventional 4-harness satin weave. Under these conditionswherein there are 14 warp ends per inch and 1 6-picl s per inch ofrelatively heavy yarn, it was essential that each pick be 'beaten upwith suificient force topabk thje .1'6.picl sinto alineal inch. t it a ti i This felt was woven as a piece and after the requisite length waswoven it was spliced to form an endless loop.

.The fabric was then placed under longitudinal tension but withoutcrosswise tension in a bath of water maintained at a temperature of 180F. for about 20 minutes in order to permit the fabric to take an initialshrinkage in the filler direction. The felt was then dried by passing itaround a rotary drier drum and an appropriately spaced idler roll. Thedistance between the idler roll and the drier drum was established so asto place the felt under tension and bring it back to its original wovenlength. The drier drum was heated to a temperature of 220 F. and washeld against rotation for approximately minutes during which the waterwas evaporated from that portion of the felt in direct contact with thesurface of the drier drum. After the water was evaporated the feltachieved a maximum temperature of about 220 F., the temperature of thedrum. At the latter temperature the crimped nylon fibers were relaxedinto the shape and position which they assumed in the woven fabric andthey become set in such relationship upon cooling of the fabric to roomtemperature. During the drying and setting operation the fabric shrunkin width and the ratio of woven width to the finished width was 140%.

The drier drum was rotated stepwise to move successive lengths of feltinto and out of direct contact with the surface thereof for drying andsetting as aforesaid until the entire length of felt has been dried andset.

The felt may be then napped and singed or otherwise processed inaccordance with known procedures which will vary with regard to theparticular use for which the felt is intended.

In its finished form the felt of this example has a weft count of 16 perinch and a warp count of 19.6 per inch. The increase in warp count isthe result of the shrinkage in the filler direction, the ratio of wovenwidth to finished width being, as stated above, 140%.

For purposes of comparison, a papermakers felt was woven from 100%natural wool fiber wherein the warp yarns weigh 700 grains per 100 yardsin the grease and the filling yarns weigh 500 grains per 100 yards. Thereed was provided with 5 dents per inch with two warp ends per dent. Thetake-up mechanism and the lay were so adjusted as to supply 16 picks perinch but it should be noted that since the filling yarns have lessweight than those used in the manufacture of the nylon felt of thepresent example, the successive picks need not be so firmly beaten up.The weave was the same conventional 4-harness satin. The fabric was thenspliced after which it was fulled in accordance with known procedure andplaced upon the drier with the tension roll so positioned as to tensionthe felt at its original woven length. The drier drum was heated to 220F. and rotated continu- 011313 to progressively dry the felt as is usualwith the manufacture of felts from natural wool. The ratio of the wovenwidth to the finished width was 200% and the finished felt bad a warpcount of 20 and a pick count of 16. The warp yarns, of course, retainedtheir original 700 grain weight and thus were completely comparable inweight with the warp yarns in the finished nylon felt of the presentexample. The filling yarns of the wool .felt weighed 500 grains whenwoven but after the reduction in width due to shrinkage and fulling, thetiller yarns are equivalent to 1000 grain yarn and thus comparable withthe final 960 grain weight of the nylon yarn used as fillers for thenylon felt. It is apparent, therefore, that the two finished felts arevery closely comparable in finished construction.

The two felts of the present example were then subiected to identicalabrasive tests on a special testing machine having d 'ven press, tensionand elongation rolls, showers, dragxbars, speed indicators and otherinstruments to simulate a press section of the common paper machine.This testing machine is particularly constructed to provide a means ofduplicating, with reasonable accuracy, the widely varying pressures,tensions, temperatures, chemical conditions and abrasive conditionswhich exist in paper machines of various types. The tests applied to thewool and nylon felts of the present example are known to be identicalwithin an accuracy of plus or minus 2% as the result of many years ofexperience with this particular testing machine.

The tensile strength of the warp and filling yarns was tested at thebeginning of the test and at frequent intervals during the progressthereof and the decrease in tensile strength was plotted against time.As might be expected, the nylon yarns exhibited tensile strength muchhigher than that of wool at the beginning of the test. As the testproceeded, the nylon warp yarns showed a rate of wear about the same asthat for the wool warp yarns but in view of their greater originalstrength the nylon warp yarns exhibited after 48 hours more than twicethe tensile strength of the wool warp yarns after about 36 hours. Warpyarns are relatively straight and protected by the filler yarns so thata felt seldom fails as a result of wear on the warp yarns. The closelypacked filler yarns present knuckles on the surfaces of the felt and aremost subject to wear from abrasion. The nylon filling yarns hadconsiderably greater tensile strength than the wool filling yarns at thebeginning of the test. as might be expected, but the rate of wear uponthe nylon was somewhat less than that upon the wool so that at the endof 48 hours the nylon filling yarns exhibited greater tensile strengththan that exhibited by the wool filling yarns after only 14 hours. Thistest indicated that the nylon felt could be expected to last almost fourtimes as long as the wool felt insofar as abrasive wear is concerned.However, the life of a felt is not solely dependent upon its resistanceto abrasion and the very much greater tensile strength of the nylon feltmakes it less vulnerable to damage from mishaps of various sorts.Therefore. the superiority of the nylon felt over the woolen one underactual conditions of use has been found to be even greater than thatindicated in the abrasion tests.

Example 2.A papermakers felt was woven in endless form from yarns havinga weight of 700 grains per yards, in the grease, for both warp and fill,the yarns being made from 100% crimped nylon fibers identical with thosedescribed above in Example 1. The reed was provided with 8 dents perinch with 4 warp ends per dent and one warp end per eye on 8 harnesses.Since the felt was being woven endless the warp count in top and bottomwas therefore 16 per inch. The take-up mechanism and lay were adjustedto supply 11 picks per inch top and bottom and thhe weave was a plainendless weave.

In this felt the woven length, i. e., the length warp-wise, becomes thefinished width and the woven width becomes the finished length. Thewoven fabric was shrunk in water at F. for about 20 minutes, with thefiller yarns maintained under tension so as to retain the original wovenwidth which was destined to become the finished length. After shrinkingthe felt was dried and set in stepwise manner as described in Example 1.The ratio of the woven length to the finished width was 116%. The amountof shrinkage was considerably less than that encountered in Example 1since, in the present example, the relatively straight warp yarns werepermitted to shrink while in Example 1 the filler yarns were permittedto shrink. The finished warp count remains at 16 per inch while thefinished filler count is increased as a result of shrinkage to 12.75 perinch.

For purposes of comparison, a similar endless felt was woven from yarnscomprising 100% natural wool fiber, the yarn weight being 640 grains per100 yards, in the grease, for the filler yarns supplied to the loom and350 grains per 100 yards, in the grease, for the warp yarns supplied tothe loom. The reed was provided with 7 dents per inch with 4 warp endsper dent and one warp end per eye in 8 harnesses. The warp count, aswoven,

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was therefore 14 per inch. The take-up motion and the lay were soadjusted as to supply 6 picksjper inch top'and bottom. After weaving,this woolen. felt was shrunk and fulled and thereafter dried inaccordance with known technique and the ratio of woven width to finishedlength was 110% and the ratio of woven length to finishedwidth was 200%.The finished warp count was 15.5 per inch and the finished filler countwas 12 per inch. Since the warp yarns were reduced to half their wovenlength by "shrinkage and fulling the finished warp yarn weight wasincreased to 700 grains; thus being comparable to the finished nylonwarp yarn Weight of the present example. The filler yarns remained at640 grains and thus are comparable to the 700 grain nylon filler yarnsof the present example.

Tests similar to those described in Example 1 indicated that the nylonfelt of the present example should last at least four times as long asthe wool felt of this example.

Example 3.-Papermakers felts identical in construction with those ofExamples 1 and 2 were made with blends of crimped nylon fibers andfibers sold under the tradename saran," the latter having a fiberdiameter lying within the range of diameters encountered in naturalwool. The proportion of saran fibers to nylon fibers may be variedconsiderably without noticeable elfect upon the durability of thefinished felt. Specifically, a blend containing 90% nylon staple fibersand saran staple fibers produces papermakers felts having all of thedesirable attributes of those of Examples 1 and 2 which in additionexhibit a desirable great tendency to pick up a freshly laid web ofpaper.

Example 4.Papermakers felts having the same desirable attributes ofthose in the preceding examples may be made in accordance with saidexamples except that the initial shrinkage is effected by exposure ofthe fabric to an atmosphere of wet steam instead of by immersion in hotwater. Thus any of said felts may be steamed in any of the several wayswhich are customarily employed for shrinkage of fabrics. A suitableprocedure is to conduct the fabric through a path wherein jets of steamare released into the atmosphere and directed onto the fabric wherebythe fabric is moistened and heated to induce shrinkage comparable tothat achieved by immersion in hot water.

Felts manufactured from synthetic resin staple fibers in accordance withthe present invention exhibit considerably greater porosity than feltsmade from natural wool and of identical construction. For this reasonand be cause the synthetic resin fibers herein availed of are usuallymuch stronger than natural wool, it is not necessary that a particularnatural wool felt be replaced by a synthetic fiber felt which isidentical, pick for pick, end for end and weight for weight. Thus insome instances it may be possible to replace a particular natural woolfelt with a synthetic fiber felt of heavier construction because of therelatively greater porosity of the synthetic fiber felt. Furthermore,the greater tensile strength of felts made from synthetic materials willmake it possible to substitute a considerably lighter construction wheremaximum porosity is particularly desired. The synthetic felts of thepresent invention greatly expand the area within which felts may bedesigned and the value of this will be apparent when it is consideredthat in many instances the design of a natural wool felt must constitutea compromise between desired porosity and requisite tensile strength.

The present application is a continuation-in-part of my applicationSerial No. 313,367, filed October 6, 1952, now abandoned.

What is claimed is:

1. The method of making papermakers wet felts from yarn composedsubstantially entirely of thermoplastic synthetic resin fibers havingcrimps which are stable below a predetermined temperature and arecapable of taking and retaining a set in addition to said crimps attemperature base are predetermined temperature a s ,ab'oye "thetemperatures ordinarily encountered in using above the temperaturesordinarily encountered in using papermakers wet felt torset the fibersin said shrunken fabric in the positions and conformations existingduring said drying and heating step while retaining substantially all ofthe original crimps therein.

2. The method of making papermakers wet felts from yarn composedsubstantially entirely of thermoplastic synthetic resin fibers havingcrimps which are stable below a predetermined temperature and arecapable of taking and retaining a set in addition to said crimps at atemperature below said predetermined temperature and above thetemperatures ordinarily encountered in using papermakers wet felt,comprising the steps of weaving a fabric tightly from said yarn,immersing said tightly woven fabric in hot water to shrink the sametransversely of the felt, applying tension to said tightly woven fabricduring said shrinking step to prevent shrinkage of the samelongitudinally of the felt, drying and heating a relatively smallportion of the shrunken fabric under longitudinal tension and at atemperature below said predetermined temperature and above thetemperatures ordinarily encountered in using papermakers wet felt to setthe fibers in said portion of the shrunken fabric in the positions andconformations existing during said drying and heating step whileretaining substantially all of the original crimps therein, andperiodically advancing said shrunken fabric under longitudinal tensionto dry and heat the entire length thereof by increments.

3. The method of making papermakers wet felts from yarn composedsubstantially entirely of thermoplastic synthetic resin fibers havingcrimps which are stable below a predetermined temperature and arecapable of taking and retaining a set in addition to said crimps at atemperature below said predetermined temperature and above thetemperatures ordinarily encountered in using papermakers wet felt,comprising the steps of weaving a fabric tightly from said yarn, heatingsaid tightly woven fabric in the presence of moisture to shrink the sametransversely of the felt, applying tension to said tightly woven fabricduring said shrinking step to prevent shrinkage of the samelongitudinally of the felt, and drying and heating the shrunken fabricunder longitudinal tension and at a temperature below said predeterminedtemperature and above the temperatures ordinarily encountered in usingpapermakers wet felt to set the fibers in said shrunken fabric in thepositions and conformations existing during said drying and heating stepwhile retaining substantially all of the original crimps therein.

4. The method of making papermakers wet felts from yarn composedsubstantially entirely of thermoplastic synthetic resin fibers havingcrimps which are stable below a predetermined temperature and arecapable of taking and retaining a set in addition to said crimps at atemperature below said predetermined temperature and above thetemperatures ordinarily encountered in using papermakers wet felt,comprising the steps of weaving a fabric tightly from said yarn, heatingsaid tightly woven fabric in the presence of moisture to shrink the sametransversely of the felt, applying tension to said tightly woven fabricduring said shrinking step to prevent shrinkage of the samelongitudinally of the felt, drying and heating a relatively smallportion of the shrunken fabric under longitudinal tension and at atemperature below said predetermined temperature and above thetemperatures ordinarily encountered in using papermakers wet felt to setthe fibers in said portion of the shrunken fabric in the positions andconformations existing during said drying and heating step whileretaining substantially all of the original crimps therein, andperiodically advancing said shrunken fabric under longitudinal tensionto dry and heat the entire length thereof by increments.

References Cited in the file of this patent UNITED STATES PATENTS1,889,902 Moore Dec. 6, 1932 2,161,766 Rugeley June 6, 1939 2,197,896Miles Apr. 23, 1940

